Architectonics of the Thalamus in the Echidna &lt;i&gt;(Tachyglossus aculeatus):&lt;/i&gt;Search for the Mediodorsal Nucleus

Regidor, José; Divac, Ivan

doi:10.1159/000118655

Cited by 13 publications

(15 citation statements)

References 24 publications

(37 reference statements)

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“…The thalamic nuclei of the echidna have been described in recent years by Welker and Lende [1980], Jones [19851 and, in part, by Ulinski [1984], In our own study [Regidor and Divac, 1987], additional observations about the thalamus in echidna can be found. In the present paper the posi tion of the labelled neurons in the thalamus is topo graphic, i.e., it does not refer to any existing labelling system.…”

Section: Histologysupporting

confidence: 66%

“…The results have shown that the large anteromediodorsal thalamic region, which in the present study contains la belled perikarya, is divisible into a medial, 'polymorphic' and a lateral, 'monomorphic' part. We have concluded that the an teromediodorsal region of the echidna thalamus consists mainly of tissue which may correspond to the MD in placentals [Regidor and Divac, 1987]. Unless the afferents of this thalamic nucleus in the echidna differ considerably from those of the MD in placental mammals, or unless the frontal cortex outside of the injected areas (e.g., the posterolateral edge and posterior parts of the ventral cortical sheet) receives other thalamic projections, our data may be taken as evidence that the cortex in front of sulcus beta in this species should be considered by definition to be the prefrontal area.…”

Section: Discussionmentioning

confidence: 81%

“…The left hemisphere indicates the findings following lateral injections. The outlines of the coronal sections are based on the Nissl series of the specimen Ta2 used in a parallel study [Regidor and Divac, 1987]. □, A = NY; □, □ = PI; □, • = BB.…”

Section: Resultsmentioning

confidence: 99%

“…The diencephalic projections to the pre frontal cortex in the echidna and eutherian mammals are difficult to compare be cause exact correspondence of the thalami of these orders has not been established [Abbie, 1934;Jones, 1985;Regidor and Divac, 1987;Ulinski, 1984;Welker and Lende, 1980;Ziehen, 1897Ziehen, , 1908. The cri teria used in our study are topography, ar chitecture and distribution of some en zymes [Regidor and Divac, 1987], These criteria are, of course, risky because of ar chitectural variations within the thalamus of nonplacental vertebrates [Riss et ah, 1972], The comparability of the intra laminar nuclei seems to be particularly difficult [Ebner, 1976;Mehler, 1969;Ulinski, 1984], We were not able to iden tify in the echidna the medioventral nu cleus which was found to project to the frontal cortex in rats under the name 'axial nucleus' in Divac et ah [1978b], see also Herkenham [1979].…”

Section: Discussionmentioning

confidence: 99%

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Afferents of the Frontal Cortex in the Echidna (Tachyglossus aculeatus). Indication of an Outstandingly Large Prefontal Area

et al. 1987

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Afferents of the large, electrically 'silent' frontal cortex in an egg-laying mammal, the echidna, were studied with the somatopetal axonal transport technique. This cortical area receives thalamic projections only from the anterior part of the antero-mediodorsal region. The medial parts of the cortex receive afferents from more medial neurons, whereas the lateral area is innervated from the laterally placed perikarya of this thalamic region. The nonthalamic afferents to the frontal cortex are, with few exceptions, similar to the afferents of the prefrontal cortex in placental mammals. Cortical afferents originate in all layers of the contralateral symmetrical areas and in the ipsilateral paleocortex, especially the cortex in the bottom of the sulcus mu. The claustrum could not be identified, neither cytoarchitecturally nor hodologically. Pending confirmation from studies of the diencephalon, we presently conclude that the large anterior cortical area in this species corresponds to the prefrontal cortex of eutherian mammals. If this conclusion is correct, the echidna is the only species studied to date that has a proportionally larger prefrontal cortex than humans.

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Section: Histologysupporting

confidence: 66%

Section: Discussionmentioning

confidence: 81%

Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

See 2 more Smart Citations

Afferents of the Frontal Cortex in the Echidna (Tachyglossus aculeatus). Indication of an Outstandingly Large Prefontal Area

et al. 1987

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“…The similar organisation of spinal nuclear groups in Eutheria and this monotreme suggests that spinal cord cytoarchitecture was highly conserved throughout radiation of the mammals, in contrast to the unique organisational features of the diencephalon and cortex in monotremes [Lende, 1964;Regidor and Divac, 1987;Krubitzer et al. 1995].…”

Section: Echidna T1 Fasciculus Gracilismentioning

confidence: 98%

Cyto- and Myeloarchitectonic Organisation of the Spinal Cord of an Echidna (Tachyglossus aculeatus)

Ashwell¹,

Zhang²

1997

Brain Behav Evol

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We have studied the cyto- and myeloarchitectural organisation of the spinal cord of an echidna (Tachyglossus aculeatus) with the aid of Nissl staining, darkfield examination and p-phenylenediamine staining. We have also examined the distribution of unmyelinated afferents by labelling with a peroxidase-conjugated lectin derived from Griffonia simplicifolia (B₄ isolectin). The cytoarchitectural features characterising the laminar organisation of the spinal cord in eutherian mammals were broadly applicable to the spinal cord of this monotreme. In addition, we identified a distinct group of large neurons in the ventral part of lamina X, extending into the ventral funiculus, that we have called the median nuclear group. We were unable to identify a central cervical nucleus in this echidna on the basis of cytoarchitectural criteria, although all other spinal cord nuclei found in eutherians could be found in this monotreme. Lectin labelling with the Griffonia simplicifolia isolectin B₄ revealed a subpopulation of dorsal root ganglion cells similar to those labelled in Eutheria. In this echidna, labelling of unmyelinated fibres was found in Lissauer''s zone and laminae I and II, as seen in rats (Rattus norvegicus); there were also deeper patches extending into laminae III to V and what appeared to be commissural axons approaching the dorsal grey commissure, which have not been seen in Eutheria. Fibre calibre in the dorsal and ventral roots of this echidna was similar to that reported in Eutheria, suggesting similar proportions of afferent fibre classes and α and γ motoneurons. In the echidna, mean diameter of myelinated dorsal root axons was 4.65 µm at T₁ and 5.22 µm at L₃, with a clear bimodal distribution in the L₃ dorsal root showing distinct groups at 1 to 5 µm and 6 to 12 µm. These made up approximately 45 and 55% of the total myelinated axon population, respectively. Myelinated fibres in the ventral root at L₃ showed two major peaks in distribution. These were at 1 to 4 µm (approximately 32% of the total myelinated fibre population) and at 7 to 14 µm (approximately 58% of the total myelinated fibre population). The cross-sectional area of the dorsal columns of this monotreme was comparable to that of a eutherian mammal of similar body weight, and myelinated axon calibre was similar to that seen in the domestic cat. Our findings indicated that spinal cord cytoarchitectural organisation is highly conserved across class Mammalia, although the lectin labelling findings suggested that termination of unmyelinated afferents in echidnas may differ from that found in Eutheria. The dorsal column system appears to be as anatomically well developed in this monotreme as in those eutherian mammals considered to have a pronounced discriminative tactile sense.

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Efferent connections of the dorsomedial thalamic nuclei of the domestic chick (Gallus domesticus)

Montagnese

Mezey

Csillag

2003

J of Comparative Neurology

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Small iontophoretic injections of the anterograde tracer Phaseolus vulgaris leucoagglutinin were placed in the thalamic anterior dorsomedial nucleus (DMA) of domestic chicks. The projections of the DMA covered the rostrobasal forebrain, ventral paleostriatum, nucleus accumbens, septal nuclei, Wulst, hyperstriatum ventrale, neostriatal areas, archistriatal subdivisions, dorsolateral corticoid area, numerous hypothalamic nuclei, and dorsal thalamic nuclei. The rostral DMA projects preferentially on the hypothalamus, whereas the caudal part is connected mainly to the dorsal thalamus. The DMA is also connected to the periaqueductal gray, deep tectum opticum, intercollicular nucleus, ventral tegmental area, substantia nigra, locus coeruleus, dorsal lateral mesencephalic nucleus, lateral reticular formation, nucleus papillioformis, and vestibular and cranial nerve nuclei. This pattern of connectivity is likely to reflect an important role of the avian DMA in the regulation of attention and arousal, memory formation, fear responses, affective components of pain, and hormonally mediated behaviors.

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Architectonics of the Thalamus in the Echidna <i>(Tachyglossus aculeatus):</i>Search for the Mediodorsal Nucleus

Cited by 13 publications

References 24 publications

Afferents of the Frontal Cortex in the Echidna (<i>Tachyglossus aculeatu</i><i>s</i>). Indication of an Outstandingly Large Prefontal Area

Afferents of the Frontal Cortex in the Echidna (<i>Tachyglossus aculeatu</i><i>s</i>). Indication of an Outstandingly Large Prefontal Area

Cyto- and Myeloarchitectonic Organisation of the Spinal Cord of an Echidna (Tachyglossus aculeatus)

Efferent connections of the dorsomedial thalamic nuclei of the domestic chick (Gallus domesticus)

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